A fuel cell includes a stack of elementary cells, within which an electrochemical reaction occurs between two reagents which are introduced continuously. The fuel, such as hydrogen, for cells operating with H2/O2 mixtures, or methanol for cells operating with methanol/oxygen mixtures, is brought into contact with the anode, while the oxidizer, generally oxygen, is brought into contact with the cathode. The anode and the cathode are separated by an electrolyte, of the proton exchange membrane type. The electrochemical reaction, the energy of which is converted into electric energy, is split into two half-reactions:                oxidation of the fuel occurring at the anode/electrolyte interface producing, in the case of cells operating with H2, H+ protons which will cross the electrolyte towards the cathode, and electrons which join the outer circuit, in order to contribute to the production of electric energy;        a reduction of the oxidizer occurring at the electrolyte/cathode interface with production of water in the case of cells operating with H2.        
The electrochemical reaction, strictly speaking, occurs at an electrode-membrane-electrode assembly.
In order to ensure the operation of electric appliances, it is necessary to obtain an electric power considerably greater than the power delivered by a single electrode-membrane-electrode assembly. In this perspective, the electrode-membrane-electrode assemblies are most often arranged as a stack, the electric continuity between the different assemblies being ensured by means of conducting plates, said bipolar plates.
In addition to the current collecting function, bipolar, plates also have to ensure the following functions:                distribution of the reagents and removal of the products at the anode and at the cathode, the reagents being hydrogen and oxygen and the products, water for cells operating with H2/O2;        removing the heat produced during the electrochemical reaction;        mechanical structuration of the stack of constitutive elementary cells of the fuel cell.        
Thus, the constitutive materials of the bipolar plates have to meet the following criteria:                sufficient electric conductivity in order to efficiently collect the electric current produced by the elementary cells;        good heat conductivity in order to remove the heat produced during the electrochemical reaction at the elementary cells;        good mechanical properties so as to be able to withstand the stresses related to the assembling of the constitutive elementary cells of the fuel cell and to also withstand handling operations during the mounting of the fuel cell;        heat stability in order to guarantee the integrity of the assembly in the ranges of the temperature of use of the fuel cell;        chemical stability with regard to the fluid present in the core of the fuel cell (for example water, acid) so as to be able to maintain the performances of the material and to avoid decomposition of the latter and thus pollution of the anode and of the cathode with which it is in contact;        impermeability to the reagents (for example, hydrogen and oxygen), greater than that of the proton exchange membrane;        surface hydrophobicity in order to facilitate discharge of the water formed during the electrochemical reaction;        capability of being shaped, so as to allow the formation of distribution channels at the surface of the plates and this preferably without requiring any machining phase for forming said channels.        
The bipolar plates presently used may be subdivided into three categories:                bipolar plates in graphite;        metal bipolar plates; and        bipolar plates in an organic composite material.        
As regards graphite plates, it is difficult to contemplate their use on an industrial scale because of their very high cost essentially due to the machining phase required for manufacturing the distribution channels.
As regards metal bipolar plates, they have a set of properties (mechanical strength, seal, electric conductivity, capability of being shaped), which make them candidates of choice for the design and making of inexpensive bipolar plates.
However, their density above that of graphite imposes their use in the form of thin sheets shaped by stamping. Under such conditions, the designs of the channels are limited (the ultimate elongation limit of the material conditioning the geometry of the channels). On top of that, the stamping technique only allows formation of channels on one face of a plate, which requires association of two stamped half plates so as to obtain a resulting plate including channels on both of its faces.
For bipolar plates made from metal sheets shaped by stamping, the arrival of the fluids and the removal of the formed products are achieved in locally planar areas of the bipolar plate, which requires the use of a frame having a suitable shape and capable of ensuring the peripheral seal, as described in WO 2007/03743. This technique has the drawback of requiring for a same bipolar plate an additional part intended to ensure the junction between two combined plates in order to form the bipolar plate and ensure supplies and removals of fluid and of product. Final bipolar plates which are less compact than expected are the result of this.
Finally, one of the problems inherent to the use of metal for forming bipolar plates lies in corrosion phenomena induced by the contact of the plates with aqueous media. In order to find a remedy to this, certain authors (such as those of the publication J. Power. Sources, 131 (2004), p. 162-168) propose the transfer of protective coatings onto said plates in order to limit the corrosion phenomenon. However, this generates a method for manufacturing the latter which is more complex to apply.
As regards the plates in organic composite materials, the latter consist in plates comprising an organic polymer matrix in which electrically conducting particles are dispersed. The particles provide the bipolar plates with electric conductivity required for collecting the current and the polymeric matrix provides the mechanical strength required for assembling the different constitutive elements of the fuel cell in which the bipolar plates are arranged.
The conducting particles may be metal particles, which has the advantage of good electric conductivity. On the other hand, they however have the drawback of having high density and of being sensitive to the chemical environment.
The conducting particles may also be carbon-based products, appearing as powders, such as carbon black, graphite powders or carbon fibers.
Conventionally, the plates are made by incorporating conductive particles into a liquid resin followed by shaping with hardening of the resin, as described in U.S. Pat. No. 6,248,467.
However, the use of a raw material as a liquid, in this case a liquid resin, causes the following drawbacks:                an instability of the system before molding because of the difficulty of controlling the cross-linking reaction of the liquid resin;        a heterogeneity of the system before molding because of the association of a liquid resin with solid particles of an electrically conducting filler;        an exudation phenomenon of the resin during the shaping of the article, which generates an article comprising a non-homogeneous distribution of the electrically conducting particles and an insulating surface of the article because of the concentration of the exudated resin at this level.        
In order to do away with these difficulties, certain authors have proposed to work from solid reagents (solid resin, conducting particles). However, the mixtures described in these documents have to be made in a molten phase before shaping, for example by hot calendering. This mixing step in the molten phase, however, generates highly significant additional expenditure, which proves to be incompatible with large scale industrialization of the manufacturing of bipolar plates. On top of that, the obtained plates do not meet the requirements of the specifications of the application notably those relating to the planar electric conductivity.
Thus, there exists a real need for articles conducting electricity, in particular bipolar plates, and methods for manufacturing the latter, which may be achieved simply, in a limited number of steps and at a lesser cost, while limiting the energy balance of these steps, compatible with an industrial application and which preferably suppress long and costly machining operations, these methods also having to give the possibility of obtaining conductive articles having efficient performances in terms of electric conductivity, of mechanical strength and of removal of the water produced over time when these are bipolar plates.